Such a sad story. It has been posted and discussed a lot on most of the RV'ing forums and camping Facebook groups that I belong to. There were many reports that their truck and trailer were seen crossing into Mexico soon after their disappearance and people wondered why the Mexican authorities would let it through with either no TIP (Temporary Import Permit) or somebody other than the registered owner of the vehicle applying for the TIP. Normally only the owner of the vehicle (not even their spouse) can apply and get one. A TIP is not needed to enter the west coast Baja area of Mexico, but it is all along the rest of the border all the way over to Brownsville. Whenever a vehicle with foreign plates passes a checkpoint, a valid TIP is the main thing the authorities (federal, state & local) are checking. I hope the family gets some support and answers from the Mexican authorities.
~Diane